Correct pressure in vehicle tyres is of considerable importance. Excessive pressure can cause premature tread wear and loss of traction in the wet. Low pressure on the other hand can cause loss of stability when cornering and tyre failure from excessive wall flexing. While most service stations provide facilities for drivers to check their tyres the gauges are often defective or at best inaccurate. In order to alleviate such problems valves have been proposed for tyres which during filling automatically cut off the air supply once a preset pressure is reached. The user therefore does not need to be concerned about monitoring tyre pressure during filling. Rather it is only necessary to maintain the air hose fitting on the tyre valve until it automatically cuts off. These valves typically use a piston which is biased to an open position by a compression spring during filling but is moved against said bias to a closed position when an applied force from the internal tyre pressure reaches a preset amount of say 200 kpa. Existing valves have the disadvantage however that the compression spring and piston are located in the base of the valve assembly which is therefore enlarged and protrudes a substantial distance through into the interior of the tyre rim. This obstructs the fitting of the tyre and can result in the base of the valve housing being damaged during initial inflation as the tyre bead expands onto the rim.